Transmission mechanism for vehicles having HST and pressure oil supply system therefor

ABSTRACT

A transmission mechanism and a pressure oil supply system therefor are provided for use in work vehicles provided with a work device externally of the body of the vehicle at longitudinal one side thereof, the transmission mechanism being simple in construction and serving to shorten the overall length of the vehicle while holding a transmission shaft interconnecting a PTO shaft and an input shaft for the work device close to a horizontal. 
     A work vehicle provided with a work device in front of the vehicle body comprises a transmission  30  disposed between a differential gear unit  10  and an HST  20  and providing a travel cooperative mechanism, a PTO shaft projecting from the housing of the HST  20 , and a PTO cooperative mechanism disposed in the housing for dividedly deriving power for the PTO shaft from the travel cooperative mechanism for the transmission of the power. The HST  20  comprises a hydraulic pump  22  having a pump shaft  22   a  for receiving an input at its rear end, and a hydraulic motor  23  having a motor shaft  23   a  for delivering a front wheel driving force and a rear wheel driving force from the front end and rear end thereof, respectively.

RELATED APPLICATION

This application claims priority to and is a continuation of U.S.application Ser. No. 10/411,526, filed Apr. 9, 2003, now U.S. Pat. No.6,830,116 which is a continuation of U.S. application Ser. No.10/185,487, filed Jun. 26, 2002 now U.S. Pat. No. 6,571,894, issued Jun.3, 2003, which is a divisional of U.S. application Ser. No. 09/485,307,filed May 15, 2000 now U.S. Pat. No. 6,457,546, issued Oct. 1, 2002which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to transmission mechanisms for vehicleshaving an HST (hydrostatic transmission), and more particularly to atransmission mechanism for work vehicles equipped with a work deviceexternally of the vehicle body, and also to a pressure oil supply systemfor the mechanism.

2. Description of the Related Technology

It is commonly demanded that various vehicles be shortened in forward orrearward length to diminish the turning radius, improve the ease ofdriving and achieve cost reductions. Especially, this is stronglydemanded of work vehicles which are equipped with a work deviceexternally of the vehicle body in front or in the rear thereof.

Work vehicles provided with a work device externally of the vehicle bodyhave a PTO shaft at a portion of the transmission for transmitting powerto the work device. With such work vehicles, it is desired that thetransmission shaft interconnecting the PTO shaft and the input shaft ofthe work device be disposed horizontally to the greatest possible extentin order to prevent the joints of the transmission shaft from giving offnoise and assure the joints of improved durability. For example, JP-U1No. 56555/1993 and JP-A No. 204135/1990 disclose transmissions for workvehicles intended to meet this demand. The disclosed arrangementsinclude pulleys or like cooperative means for positioning a PTO shaft1103 at a lower level than a front axle 1105 to cause the shaft toproject from the front end face of the front axle case (as indicated atX in FIG. 19). Generally, the transmission shaft 1104 for a work device1106 needs to be lengthened (as indicated at Y in FIG. 19) if it isattempted to position the transmission shaft 1104 closer to a horizontalwhile causing the PTO shaft 1103, as positioned approximately at thesame level as the engine drive shaft 1101 a, to project from the frontend of the front axle case, consequently increasing the overall vehiclelength. Alternatively, the transmission shaft 1104 must be inclined (asindicated at Z in FIG. 19) if an attempt is made to shorten the overallvehicle length while causing the PTO shaft 1103 to project from thefront end of the front axle case at substantially the same level as theengine drive shaft 1101 a, consequently increasing the load on thetransmission shaft and impairing the durability of the transmissionshaft. In view of these structural drawbacks, the transmissionsdisclosed in the foregoing publications are so constructed as statedabove.

In the case of the conventional construction described, however, adifferential gear unit is to be interposed between the engine outputshaft (or HST motor shaft) and the PTO shaft, so that the cooperativemechanism between the two shafts must be adapted to avoid theinterference with the differential gear unit. This results in anincrease in the vehicle cost and an impaired maintenance workefficiency.

With vehicles, especially with work vehicles, it is known to dividedlyderive a rear wheel driving force from the output of an HST for drivingthe front wheels. JP-A No. 66749/1997, for example, discloses such atransmission mechanism. With reference to FIG. 20 showing such aconventional transmission mechanism as is disclosed in this publication,a vehicle comprising a differential gear unit 1140, HST 1120 and drivesource 1110 which are arranged from the front of the vehicle rearwardhas a transmission 1130, in which a driving force from the drive sourceis divided into a front wheel driving force and a rear wheel drivingforce. This construction has the following drawbacks. Incidentally,indicated at 1131 in the drawing is a front wheel drive shaft which iscoupled to the differential gear unit 1140 for driving front axles 1151,and at 1132 is a rear wheel drive shaft which is connected to a rearaxle 1152 by an unillustrated transmission shaft.

The transmission mechanism shown in FIG. 20 essentially requires thetransmission 1130, which increases the number of parts and the cost. Theprovision of the transmission 1130 further entails the problem ofimpairing the reliability of the vehicle. Since the transmission 1130serves as a power transmission path for both the front wheel drivingforce and the rear wheel driving force, the components of thetransmission are burdened with a great load. Accordingly, the gears andother components are susceptible to damage, which lowers the reliabilityof the vehicle. Furthermore, the transmission 1130 is provided in alimited space between the differential gear unit 1140 and the HST 1130,necessitating difficult installation work, which leads to the problemthat the vehicle is inefficient to assemble in its entirety.

With work vehicles equipped with a work device externally of the vehiclebody, there is a need to provide a considerable distance between theengine and the HST because it is necessary to interconnect the drivesource and the HST by means of universal joints. Stated morespecifically, the drive source is installed on the vehicle body withrubber vibration isolators interposed therebetween, while the HST isconnected to the differential gear casing which is fixed to the frontaxle cases. A vibration difference therefore occurs between the drivesource and the HST. Accordingly, to interconnect the two components by ashaft with the vibration difference absorbed, universal joints are usedfor the shaft to be connected between the drive source and the HST. Forthis reason, there is a need to provide a distance permitting thearrangement of two universal joints in series between the HST and thedrive source.

With vehicles wherein a PTO unit is provided which has a PTO shaft for amower or like work device, and a hydraulic clutch for effecting orinterrupting the transmission of the output of the PTO shaft, it isdesired to position the PTO shaft inwardly of the vehicle body to thegreatest possible extent while shortening the distance between thehydraulic clutch and a charge pump for supplying a hydraulic fluid tothe clutch.

A shorter distance between the pump and the clutch is desirable becauseof the difficulty to be encountered in hydraulically controlling theclutch if the distance is great. Inward positioning of the PTO shaft isdesirable in order to reduce the overall length of the vehicle includingthe mower or the like while horizontally positioning the connecting rodbetween the shaft and the mower or the like.

This will be described with reference to a front mount mower tractorwhich is equipped with a mower in front of the vehicle body. If it isattempted to shorten the overall length of the vehicle including themower in an arrangement wherein the PTO shaft is caused to projectforward from the front axle case, the transmission shaft interconnectingthe PTO shaft and the mower must be given a great inclination. Thetransmission shaft is pivotally moved vertically when the mower israised or lowered. If the inclination of the transmission shaft isgreater, the angle through which the shaft is pivotally moved alsoincreases, permitting the transmission shaft joints to produce a loudernoise and impairing the durability of the joints. It is thereforedesired that the PTO shaft be disposed inward longitudinally of thevehicle body (toward the rear of the vehicle body in the case of thefront mount mower tractor) in order to shorten the overall length of thevehicle while obviating these drawbacks.

Thus, it is desired that the vehicle wherein the power of the drivesource is transmitted to the travel device and to the PTO unit via theHST fulfill the foregoing requirements, whereas transmission mechanismsstill remain to be developed which meet all of these requirements.

Conventionally, the following construction has been adopted for thepressure oil supply system for supplying a hydraulic fluid to powersteering hydraulic devices or to hydraulic devices for lifting workdevices such as mowers. The conventional pressure oil supply system hasan arrangement wherein a hydraulic pump for supplying the pressure oilis attached to the drive source of the vehicle, and the casing of thedifferential gear unit is used also as an oil tank serving as the oilsupply source for the hydraulic pump. The pump shaft of the hydraulicpump can be coupled to the drive source easily, while the use of thecasing eliminates the cost increase and the increase of the vehicle sizethat would result if an oil tank for specific use is provided.

However, this arrangement requires an elongated inflow lineinterconnecting the hydraulic pump and the casing, consequently offeringthe piping increased resistance which is liable to impair the operationefficiency of the pump. Although the inflow line can be given anincreased diameter to reduce the piping resistance, this will entail anincreased cost.

The drive source is installed in the vehicle body with use of rubbervibration isolators, while the casing is fixed to the axle case, so thata vibration difference occurs between the hydraulic pump attached to thedrive source and the casing. This results in the necessity of using aflexible tube or like pipe which is capable of absorbing the vibrationdifference between the pump and the casing for the inflow line forholding these two components in communication, hence a higher cost.

In order to shorten the distance between the hydraulic pump and the oiltank, it is possible to install a specific tank in the vehicle, aspositioned in a vacant space in the vicinity of the drive source, butthe installation of the specific tank leads to a higher cost and agreater vehicle size. Use of such a tank still involves the problem ofvibration difference between the oil tank and the hydraulic pump.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

A first object of the present invention is to provide a transmissionmechanism which is simple in construction for use in work vehiclesequipped with a work device externally of the vehicle body, thetransmission mechanism being adapted to shorten the overall length ofthe vehicle.

A second object of the invention is to provide a transmission mechanismfor use in such work vehicles which is adapted to shorten the overalllength of the vehicle body while permitting a transmission shaft to bepositioned close to a horizontal for interconnecting a PTO shaft fordriving the work device and the input shaft of the work device.

A third object of the invention is to provide a transmission mechanismof simple construction for the front wheels and rear wheels of vehiclesincluding an HST, the transmission mechanism comprising components whichare rendered free of excessive loads.

A fourth object of the invention is to provide a transmission mechanismwhich realizes at the same time a vehicle of shortened overall length,positioning of a PTO shaft longitudinally inwardly of the vehicle bodyand provision of a sufficient distance between the drive source and anHST.

A fifth object of the invention is to provide a pressure oil supplysystem of simple construction for a hydraulic device for use in vehicleshaving the hydraulic device, the system being adapted to render thevehicle compact and less costly.

To fulfill the foregoing objects, the present invention provides atransmission mechanism for a work vehicle having a differential gearunit, an HST and a drive source which are arranged in a body of thevehicle from longitudinal one side of the vehicle body, i.e., one sidethereof in a first direction, toward the other side thereof in a seconddirection so as to drive axles positioned toward said one side, thevehicle having a work device disposed externally of the vehicle bodytoward the first direction, the transmission mechanism beingcharacterized in that the mechanism comprises:

-   -   a travel power transmission path for transmitting power from the        drive source to the differential gear unit via the HST, and a        PTO power transmission path for dividedly transmitting the power        from the travel power transmission path to a PTO unit for        driving the work device,    -   the travel power transmission path further comprising a        transmission for transmitting an output of the HST to the        differential gear unit,    -   the transmission constituting a portion of the travel power        transmission path and having a casing, and an input portion for        receiving the power from the drive source, an output portion        coupled to the differential gear unit and a travel cooperative        mechanism coupling the input portion to the output portion which        are housed in the casing,    -   the HST comprising a hydraulic pump having a pump shaft        extending longitudinally of the vehicle body, a hydraulic motor        having a motor shaft rotatable in cooperation with the hydraulic        pump, and an HST housing accommodating the hydraulic pump and        the hydraulic motor therein, the pump shaft having one end        extending outward from the HST housing in the second direction        and being connectable to a shaft of the drive source, the motor        shaft having one end extending in the first direction into the        transmission casing and connected to the input portion of the        transmission,    -   the PTO unit comprising a PTO shaft supported by the HST housing        so as to extend from the HST housing in the first direction, and        a PTO cooperative mechanism accommodated in the HST housing and        coupling the pump shaft to the PTO shaft to provide the PTO        power transmission path (first feature of the invention).

To fulfill the foregoing objects, the present invention also provides atransmission mechanism comprising a differential gear unit, an HST and adrive source which are arranged in a body of a vehicle from longitudinalone side of the vehicle body, i.e., one side thereof in a firstdirection, toward the other side thereof in a second direction so as todrive axles positioned toward said one side, the transmission mechanismbeing characterized in that:

-   -   the HST comprises a hydraulic pump having a pump shaft extending        longitudinally of the vehicle, a hydraulic motor cooperative        with the hydraulic pump and having a motor shaft disposed in        parallel to the pump shaft, and a housing accommodating the        hydraulic pump and the hydraulic motor therein,    -   the hydraulic pump being adapted to receive power from the drive        source by the pump shaft at an end thereof toward the second        direction,    -   the hydraulic motor being adapted to output a driving force to        be delivered to the differential gear unit from the motor shaft        at an end thereof toward the first direction and to output a        driving force to be delivered to wheels toward the second        direction from the motor shaft at an end thereof toward the        second direction (second feature of the invention).

To fulfill the foregoing objects, the present invention further providesa transmission mechanism for a vehicle so adapted that power from adrive source installed in a body of the vehicle is transmitted to atravel device and a PTO unit via an HST disposed outwardly of the drivesource in a longitudinal direction of the vehicle, the transmissionmechanism being characterized in that:

-   -   the mechanism comprises the HST for receiving a driving force        from the drive source, and the PTO unit for receiving an output        from the HST,    -   the PTO unit comprising a PTO shaft, a hydraulic clutch for        effecting or interrupting power transmission to the PTO shaft, a        charge pump for supplying a hydraulic fluid to the clutch, and a        hydraulic circuit for interconnecting the clutch and the charge        pump,    -   the HST comprising a hydraulic pump having a pump shaft        extending longitudinally of the vehicle and connected at an        inward end thereof to a shaft of the drive source, a hydraulic        motor having a motor shaft rotatable in cooperation with the        hydraulic pump, and a housing accommodating the hydraulic pump        and the hydraulic motor therein, the pump shaft having an        outward end projecting from the housing outward longitudinally        of the vehicle, the housing having a main body accommodating the        hydraulic pump and the hydraulic motor therein, and an extension        extending outward widthwise of the vehicle from a side of the        main body at which side the hydraulic pump is positioned,    -   the charge pump having a casing liquid-tightly surrounding the        projection of the pump shaft and being adapted to perform a        pumping action for the clutch by the rotation of the pump shaft,    -   the PTO shaft being supported by the housing extension        longitudinally of the vehicle and having an outer end projecting        outward longitudinally of the vehicle,    -   the hydraulic clutch being supported by the PTO shaft within the        housing extension (third feature of the invention).

To fulfill the foregoing objects, the present invention further providesa pressure oil supply system for a vehicle comprising a hydraulicdevice,

-   -   the vehicle being so adapted that power from a drive source        installed in a body of the vehicle is transmitted to a drive        axle via an HST disposed adjacently to the drive source along        the longitudinal direction of the vehicle and via a differential        gear device coupled to the HST along said longitudinal        direction,    -   the HST comprising an HST pump having a pump shaft extending        longitudinally of the vehicle and connected to the drive source        by a shaft, an HST motor cooperative with the hydraulic pump and        having a motor shaft, and a housing accommodating the HST pump        and the HST motor therein,    -   the differential gear device having a casing supporting the        drive axle, and a differential gear unit housed in the casing        and operatively connected to the motor shaft,    -   the pressure oil supply system being characterized in that the        system comprises:    -   a hydraulic pump having a drive shaft supported by the housing        so as to cause one end thereof to project outward from the        housing, and a pump case formed continuously with the housing so        as to liquid-tightly surround the projecting end of the drive        shaft, the hydraulic pump being adapted to perform a pumping        action by the rotation of the drive shaft,    -   a hydraulic output cooperative mechanism coupling the pump shaft        of the HST pump to the drive shaft,    -   an intake line having one end connected to the casing of the        differential gear device and the other end connected to the pump        case, and    -   a discharge line having one end connected to the pump case and        the other end connected to the hydraulic device (fourth feature        of the invention).

The transmission mechanism can be so characterized that the HSTcomprises a hydraulic pump having a pump shaft extending longitudinallyof the vehicle, a hydraulic motor cooperative with the hydraulic pumpand having a motor shaft disposed in parallel to the pump shaft, and ahousing accommodating the hydraulic pump and the hydraulic motortherein, the housing having walls spaced apart from each other andpositioned toward the first direction and toward the second directionrespectively, the transmission further comprising, between thefirst-direction wall and the second direction wall, a PTO unit, and aPTO power transmission path for transmitting devidedly to the PTO unitthe power to be delivered from the drive source to the HST.

Alternatively, the transmission mechanism can be so characterized thatthe HST comprises a hydraulic pump having a pump shaft extendinglongitudinally of the vehicle for receiving a driving force from thedrive source, a hydraulic motor cooperative with the hydraulic pump andhaving a motor shaft disposed in parallel to the pump shaft foroutputting a driving force for travel, and a housing accommodating thehydraulic pump and the hydraulic motor therein, the housing having aspace accommodating the pump and the shaft therein and serving as areservoir for lubricating oil, the housing further accommodating a PTOunit, and a PTO power transmission path for transmitting devidedly tothe PTO unit the power to be delivered from the drive source to the HST,the PTO unit comprising a clutch for effecting or interruptingtransmission of the driving force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side elevation of a front mount mower tractorcomprising a transmission mechanism according to the invention.

FIG. 2 is a perspective view showing a mechanism for driving the frontand rear wheels of the tractor of FIG. 1.

FIG. 3 is a view of the tractor as it is seen in the direction of arrowA in FIG. 2.

FIG. 4 is a plan view in development and in section showing a firstembodiment of transmission mechanism of the invention.

FIG. 5 is a view in section chiefly showing an HST and a PTO unit ofFIG. 4.

FIG. 6 is a view in section taken along the line VI—VI in FIG. 4.

FIG. 7 is a view in section taken along the line VII—VII in FIG. 4.

FIG. 8 is a view in section taken along the line VIII—VIII in FIG. 4.

FIG. 9 is a view in section taken along the line IX—IX in FIG. 4.

FIG. 10 is a view in section taken along the line X—X in FIG. 4.

FIG. 11 is a view in section taken along the line XI—XI in FIG. 4.

FIG. 12 is a view in section taken along the line XII—XII in FIG. 4.

FIG. 13 is a view in section taken along the line XIII—XIII in FIG. 5.

FIG. 14 is a hydraulic circuit diagram of the transmission mechanismshown in FIG. 4.

FIGS. 15 to 18 are sectional views showing modifications of thetransmission mechanism shown in FIG. 4.

FIG. 19 is a side elevation schematically showing a conventionaltransmission mechanism.

FIG. 20 is a plan view schematically showing a conventional transmissionmechanism.

BEST MODE OF CARRYING OUT THE INVENTION

The preferred embodiment of transmission mechanism of the invention willbe described below with reference to the accompanying drawings. FIG. 1is a schematic side elevation of a front mount mower tractor 100 havingincorporated therein the transmission mechanism of the embodiment.

General Description of Mower Tractor

The front mount mower tractor 100 will be described first with referenceto FIG. 1.

In the following embodiment, a first direction along the length of thevehicle body will be referred to as “front,” and a second directiontherealong as “rear.” However, these directions can be in reversed whenso required.

The mower tractor 100 comprises a vehicle body 101, front wheels 102 andrear wheels 103 arranged respectively at a front portion and a rearportion of the vehicle body, and a mower 104 disposed in front of thevehicle body. Arranged at a lower portion of the vehicle body 101 are adifferential gear unit 10 for driving front axles 120, an HST 20 and adrive source 90 which constitute the transmission mechanism of thepresent embodiment. A transmission 30 is disposed between thedifferential gear unit 10 and the HST 20. Indicated at 80 in the drawingis a hydraulic block (center section) formed with oil channels for theHST, etc. According to the present embodiment, the HST 20 and the gearunit 10 are interconnected by the hydraulic block 80. With this vehicle,a front mower lift unit 105 a and a power steering unit 105 b areincluded in the hydraulic unit.

The driver's seat of the mower tractor 100 is provided with a masterbrake pedal coupled to brakes (indicated at 205 in FIG. 4) providedrespectively on the left and right axles for actuating these brakes atthe same time, turn brake pedals L and R for operating these brakesindependently, and a speed change pedal 112 coupled to a hydraulic pump(indicated at 22 in FIG. 4) included in the HST 20. (The drawing showsthe turn brake pedal (left) 111, and the turn brake pedal (right) andthe master brake pedal are positioned behind and away from the plane ofthe drawing.) The speed change pedal 112 (see FIG. 1) has a toe pedalmember which accelerates the vehicle forward when stepped on, and a heelpedal member which accelerates the vehicle rearward when stepped on. Thedriver's seat of the mower tractor 100 is further provided with a manuallever 113 which is pivotally movable forward and rearward over apredetermined distance. Depending on the pivotally moved position, aswitch (not shown) is turned on or off, giving an on or off signal forcontrolling a solenoid valve (not shown) to engage or disengage the PTOclutch to be described later. Indicated at 115 are support pointsprovided on the left and right axle cases at the bottom side thereof forsuspending the mower 104.

FIG. 2 shows a mechanism for driving the front and rear wheels of thetractor of FIG. 1. Power is input to the mechanism from an engine (notshown) disposed in the rear of the HST 20 in the drawing. A front wheeldriving force is delivered to the front axles 120 via the differentialgear unit 10 disposed in front of the HST 20. On the other hand, a rearwheel driving force is delivered from a rear wheel output shaft 24 aprovided in the rear of the HST to rear axles 130 through a transmissionshaft 125. The drawing shows the hydraulic block 80, a charge pumpindicated at 55 and a PTO shaft indicated at 41 and provided at a frontportion of the vehicle for driving the mower.

FIG. 3 is a view of the mechanism as it is seen in the direction ofarrow A in FIG. 2, FIG. 4 is a cross sectional view in developmentshowing an arrangement including the HST, PTO unit and rear wheel outputportion, and FIGS. 7 to 13 are views in sections taken along therespective lines VII—VII to XIII—XIII in FIG. 4.

General Description of Transmission Mechanism

The transmission mechanism according to the present embodiment will bedescribed next. As shown apparently in FIG. 4, the transmissionmechanism of the present embodiment comprises a differential gear unit10 for driving the front axles 120, HST 20 and drive source (not shownin FIG. 4) which are arranged from the front of the vehicle bodyrearward within the vehicle body, and a transmission 30 is disposedbetween the gear unit 10 and the HST 20. Indicated at 121 in the drawingis a front axle case housing each front axle 120, at 80 a hydraulicblock formed with oil channels for the HST 20, and at 205 a brake forbraking the rotation of each of the left and right axles.

Differential Unit

With reference to FIG. 4, the differential unit 10 comprises a housing12 joined to the opposite front axle cases 121 at the widthwisemidportion of the vehicle body, a set of planetary gears enclosed in thehousing and cooperative with the opposite front axles 120 and an inputgear 11 which is a crown gar cooperative with the planetary gear set.The input gear 11 is in mesh with teeth on an output shaft 33 of thetransmission 30 to be described later for power transmission.

HST

The HST 20 comprises a housing 21, hydraulic block 80, and variabledisplacement hydraulic pump 22 of the axial piston type and fixeddisplacement hydraulic motor 23 of the axial piston type which aresupported by the block and encased in the housing 21.

The housing 21 has a main body 21 a located in approximately the sameposition as the differential gear unit 10 with respect to the widthwisedirection of the vehicle body, and an extension 21 b extending leftwardfrom the main body 21 a. The hydraulic pump and motor 22 and 23 areaccommodated in the housing main body 21 a. Encased in the housingextension 21 b is a PTO unit 40 for driving the mower. Incidentally, theterms left and right are used for the present embodiment as the vehicleis seen from the rear forward.

The housing 21 is in the form of a cube having a rear wall extendingwidthwise of the vehicle, left and right side walls extending forwardfrom opposite ends of the rear wall, and a front wall interconnectingthe forward ends of the side walls. The front wall has an opening in theregion thereof corresponding to the main body, while the rear wall hasan opening in the region thereof corresponding to the extension. Thus,the main body 21 a of the housing is open toward the front and has arear side closed with the rear wall. On the other hand, the extension 21b is closed with the front wall at its front side and open at its rearside. The front opening of the main body 21 a is closed with thehydraulic block 80, and the rear opening of the extension 21 b is closedwith a closing member 21 c. This provides the following advantage. Ifboth the main body 21 a and the extension 21 b are opened at their frontsides in the structure comprising the extension 21 b in addition to thebody 21 a, there arises a need to increase the length of the hydraulicblock 80 widthwise of the vehicle body for closing the opening to entaila cost increase due, for example, to an increase in the amount ofmaterial. The hydraulic block 80 requires a considerable thickness so asto withstand the pressure of the hydraulic fluid circulating through thepump 22 and motor 23, so that the amount of material increased byincreasing the widthwise length of the block 80 increases in proportionto the thickness. Further the housing 21 having the structure describedcan be cast easily by removing the mold for the main body 21 a forward,and the mold for the extension 21 b rearward.

The PTO shaft 41 is supported at two points within the HST housingextension 21 b by a bearing mounted on the front wall of the extension21 b and a bearing mounted on the closing member 21 c.

As shown in FIG. 4 and FIG. 9 which is a view in section along the lineIX—IX in FIG. 4, the hydraulic pump 22 has a pump shaft 22 a extendinglongitudinally of the vehicle body. The hydraulic pump 22 is of thevariable displacement type having a swash plate for giving a variabledisplacement. The swash plate is connected to the speed change pedal 112disposed in the vicinity of the driver's seat by a swash plate couplingpin 26 a (see FIGS. 2 and 3) supported by the housing 21, an arm 26 boperatively connected to the pin 26 a and a suitable connecting member(not shown) such as a wire. The pump shaft 22 a has a rear endprojecting rearward from the housing 21 and connected to the outputshaft of the unillustrated engine by a universal joint. The pump 22 ahas a front end projecting forward from the housing 21 and extendingthrough the hydraulic block 80 to transmits power to the charge pump 55.A gear 22 c is nonrotatably supported by the pump shaft 22 a at theportion thereof positioned rearwardly of the swash plate.

The shaft 23 a of the hydraulic motor 23 has a front end portionprojecting forward from the housing 21, extending through the block 80and coupled to an input gear 11 of the differential gear unit 10. Themotor shaft 23 a has a rear end portion projecting rearward from thehousing 21 for delivering rear wheel driving force to a rear wheeloutput unit 24.

Further according to the present embodiment, the pump shaft 22 a and themotor shaft 23 a are arranged approximately in the same horizontalplane, thereby making it possible to dispose the engine at a lower levelfor connection to the pump shaft 22 a by a shaft and to lower the centerof gravity of the vehicle to give improved stability to the vehicle. Inthe conventional arrangement wherein the pump shaft 22 a to be connectedto the drive shaft of the engine is positioned above the motor shaft 23a, the engine is positioned at a higher portion of the vehicle,consequently raising the center of gravity of the vehicle and impairingthe stability of the vehicle, whereas the present embodiment is free ofsuch a drawback.

Although the HST housing main body 21 a is integral with its extension21 b according to the present embodiment, these components can beseparate members like the transmission casing 31 to be described below.

Transmission

The transmission 30 comprises a casing 31, an input gear 34 serving as atransmission input portion for receiving within the casing 31 the powerdelivered from the engine via the HST 20, and an output gear 33 aproviding a transmission output portion for delivering the power to theinput gear 11 of the differential gear unit 10. The casing 31 ispositioned as held between the gear unit 10 and the HST housing mainbody 21 a. An output shaft 33 is supported by the casing 31 and providedwith an input gear 35 and the output gear 33 a for transmitting thedrive force to the opposite front axles 120.

PTO Unit

As shown in FIG. 4, FIG. 5 and FIG. 11 which is a view in section alongthe line XI—XI in FIG. 4, the PTO unit 40 comprises the PTO shaft 41which is supported by the front wall of the housing extension 21 b andthe closing member 21 c and which has a front end portion projectingforward from the extension 21 b, a driven member (clutch member) 42supported by the PTO shaft nonrotatably but axially slidably, and adrive member (gear 43 b) meshing with the gear 22 c and supported by thePTO shaft 41 rotatably but axially nonslidably. The clutch of the PTOunit is engaged or disengaged by the pressure of the hydraulic fluidsent forward from the charge pump 55 through an oil channel (PTO line67) formed in the hydraulic block 80, housing 21 and closing member 21c. Indicated at 69 in the drawing is an accumulator which is provided inthe PTO line 67 and which functions as a hydraulic shock absorbingmember for preventing the oil from the charge pump 55 from actingabruptly to smoothly engage the clutch 45.

Power Transmission Path for Travel

With reference to FIGS. 4 and 9, a description will be given first of atravel power transmission path extending from the engine to thedifferential gear unit 10 and included in the transmission mechanismthus constructed. As already described, the rear end portion of the pumpshaft 22 a projects rearward from the HST housing 21 and is connected atthe projecting portion to the engine output shaft by a transmissionshaft and a universal joint. On the other hand, the front end portion ofthe motor shaft 23 a extends into the main body 31 a of the transmissioncasing, providing a transmission input shaft 32 nonrotatably joined tothe input shaft 34. According to the present embodiment, the motor shaft23 a and the transmission input shaft are provided by a common shaft,whereas an independent input shaft can be provided as supported by thecasing main body 31 a and connected to the motor shaft 23 a nonrotatablyabout the axis, with the input shaft 34 nonrotatably mounted on theinput shaft. In this case, the independent input shaft and the inputgear nonrotatably supported thereby provide the transmission inputportion.

The output gear 33 a is nonrotatably provided on the output shaft 33.The output shaft 33 is supported above the differential gear unit 10 andextends widthwise of the vehicle body as seen in FIG. 4. The gear 35 isfurther supported by the output shaft 33. The gear 35 is in mesh withthe gear 34 on the input shaft 32.

Thus according to the present embodiment, a travel cooperative mechanismfor transmitting the drive force of the engine to the differential gearunit 10 is provided by the HST 20 including the pump shaft 22 a and themotor shaft 23 a, input shaft 32, input gear 34 nonrotatably supportedby the input shaft 32, gear 35 meshing with the input gear 34, outputshaft 33 nonrotatably supporting the gear 35 thereon, and output gear 33a nonrotatably provided on the output shaft 33 and meshing with theinput gear 11 of the differential gear unit.

PTO Power Transmission Path

With reference to FIGS. 4, 5, 7 and 11, a description will be given nextof a PTO transmission path for deriving power from the travel powertransmission path and transmitting the power to the PTO shaft. As shownin FIG. 4, the pump shaft 22 a within the HST housing 21 has the gear 22c supported on a portion thereof rearward from the hydraulic pump mainbody and nonrotatably relative to the shaft. The gear 22 c is in meshwith the gear 43 b of the clutch 45 to be described later. The gear 43 bis supported by the PTO shaft 41, with the clutch driven member (clutchmember) 42 interposed therebetween. Thus, a PTO cooperative mechanismfor transmitting power from the pump shaft 22 a to the PTO shaft 41 isprovided by the gear 22 c nonrotatably supported by the pump shaft 22 a,clutch 45 in engagement with the gear 22 c and the driven member 42.

The present embodiment includes a brake member 46 disposed in the rearof the closing member 21 c and operatively connected to the clutchmember 42 as shown in FIGS. 4, 5, and 11, such that the brake isreleased when the clutch is engaged, or conversely the brake is actuatedwhen the clutch is disengaged. The brake member 46 thus provided stopsthe rotation of the mower against the force of inertia thereofsimultaneously when the drive force for the mower is cut off.

The present embodiment thus constructed has the following advantage. Ifthe PTO shaft is caused to project forward from the front axle case at aposition above the front axle, with the front end of the front mowerpositioned at the same distance from the case as in the presentembodiment, the transmission shaft connecting the PTO shaft to the mowerinput shaft has an increased inclination (see FIG. 19, Z). The increasedinclination of the transmission shaft impairs the durability of thejoints of the transmission shaft and produces a louder noise, forexample, when the mower is raised or lowered.

On the other hand, it is extremely difficult to cause the PTO shaft toproject forward from the front axle case at a position below the frontaxle (see FIG. 19, X) because of the presence of the support point for aworking machine lift link disposed to the front of the front axle case,making complex the PTO cooperative mechanism for dividedly derivingpower from the travel power transmission path and delivering the powerto the PTO shaft and resulting in a cost increase and difficultmaintenance. If caused to project from a position below the lift linksupport point, the PTO shaft greatly diminishes the ground clearance ofthe transmission shaft, rendering the transmission shaft liable tocontact stones or like obstacles on the terrain and further entailingthe drawback that the inclination of the transmission shaft becomesexcessively great when the working machine is lifted.

In contrast, the PTO shaft 41 of the present embodiment is supported on,and caused to project from, the HST housing positioned rearwardly of thefront axle 120, and the shaft 41 is coupled to the pump shaft 22 a by agear transmission assembly within the HST housing 21. This simplifiesthe construction of the PTO operative mechanism for deriving power fromthe travel power transmission path and delivering the power to the PTOshaft 41, further permitting the PTO shaft 41 to be disposed in the rearof the front axle 120, whereby the overall length of the vehicleincluding the mower can be shortened with a decreased inclination givento the transmission shaft interconnecting the PTO shaft and the mowerinput shaft.

Further with the PTO shaft 41 projecting from the HST housing extension21 b in the present embodiment, the pump shaft 22 a and the motor shaft23 a can be arranged in approximately the same horizontal plane, so thatthe engine coupled to the pump shaft 22 a can be disposed at a lowerposition in the vehicle, consequently lowering the center of gravity ofthe vehicle to give improved stability to the vehicle.

Rear Wheel Output Transmission Path

Next, a transmission path for the rear wheel drive output shaft 24 awill be described with reference to FIGS. 4 and 10. A rear wheel outputunit 24 is disposed to the rear of the HST 20 at the right side thereof.The output unit 24 has a case 24 b joined to the housing 21. This casehas an inward portion 241 overlapping the portion of the housing rearwall which portion supports the rear end of the motor shaft, and anoutward portion 242 extending rightward from the inward portion so as tobe positioned externally of the housing 21 widthwise of the vehicle. Theoutward portion 242 has a forwardly bulging part 242 a.

Supported by the case 24 b are an input shaft 24 d, intermediate shaft24 e and rear wheel drive shaft 24 a which extend longitudinally of thevehicle and are arranged in the direction of from the inward portion 241toward the outward portion 242. The input shaft 24 d is connected at itsfront end to the motor shaft 23 a nonrotatably about the axis. An inputgear 24 f is mounted on the input shaft 24 d nonrotatably relativethereto. The intermediate shaft 24 e carries thereon an intermediategear 24 g nonrotatable relative thereto and meshing with the input gear24 f.

On the other hand, the rear wheel drive shaft 24 a has a rear endportion projecting rearward from the case 24 b. The power for drivingthe rear wheels can be taken off from this portion. A clutch mechanism24 h is supported by the drive shaft 24 a utilizing the bulging part 242a of the case. According to the present embodiment, the input gear 24 f,intermediate shaft 24 e, intermediate gear 24 g and clutch mechanism 24h provide a cooperative mechanism for transmitting the power from theinput shaft 24 d to the rear wheel drive shaft 24 a.

The clutch mechanism 24 h comprises a one-way clutch 24 i and a lockmember 24 j for the clutch. The one-way clutch 24 i has an outer wheel243 formed on its outer periphery with a gear meshing with theintermediate gear 24 g, and a clutch element 244 provided between theouter wheel 243 and the drive shaft 24 a for transmitting only anadvancing force to the drive shaft 24 a. On the other hand, the lockmember 24 j is provided on the drive shaft 24 a nonrotatably and axiallyslidably and has a shifter 245 disengageably engageable with the outerwheel 243.

The clutch 24 h prevents the rear wheels from skidding owing to adifferent in turning radius between the front wheel and the rear wheelduring a forward drive and provides a four-wheel reverse drive. Statedmore specifically, the one-way clutch 24 h is actuated for forwarddrives, permitting the rear wheel drive shaft 24 a to rotate at a higherspeed than the outer wheel 243 and consequently preventing the rearwheels from skidding owing to the turning radius difference between thefront and rear wheels. On the other hand, the one-way clutch 24 h islocked by the rock member 24 j for reverse drives, whereby the drivingforce for the rear wheels can be output effectively.

Further according to the present embodiment, the clutch mechanism 24 his installed in a vacant space available at the right side of the HST 20and in the rear of the differential gear unit 10. The provision of theclutch mechanism 24 h therefore leads to no increase in the size of thevehicle.

Further because the rear wheel drive shaft 24 a is positionedrightwardly away from the motor shaft 23 a as previously stated, theengine can be installed at a lower level. In the case where the rearwheel drive shaft 24 is disposed in alignment with the motor shaft 23 a,the engine needs to be installed at a higher level so as to avoidinterference of the transmission shaft 125 for interconnecting the driveshaft 24 a and the rear axles 130 with the engine (see FIG. 2). Theengine thus positioned at the higher level makes the vehicle greater insize and impairs running stability owing to a rise in the center ofgravity of the vehicle, whereas if the drive shaft 24 a is positionedrightwardly away from the axis of the motor shaft 23 a as in the presentembodiment, no interference occurs between the transmission shaft 125and the engine even if the engine is installed at approximately the samelevel as the HST 20, consequently obviating the drawback that thevehicle becomes greater in size and impaired in running stability.

FIG. 15 shows the main components of a transmission path for the rearwheel output which are different in arrangement from those shown in FIG.4. The arrangement of FIG. 15 differs from that of FIG. 4 in thefollowing respects. In FIGS. 15 and 4, like parts are designated by likereference numerals. The illustrated casing of a transmission 300 has amain body 310 held between the differential unit 10 and the HST housingmain body 21 a, and an extension 311 extending from the main body 310 ina direction (rightward in the illustration) opposite to the HST housingextension 21 b widthwise of the vehicle body. A first intermediate shaft351 disposed on the same axis as the output shaft 33 is supported by thetransmission casing extension 311. The first intermediate shaft 351 andthe output shaft 33 are butted against each other and made nonrotatableabout the axis relative to each other by a coupling member 352. A gear353 is supported on the first intermediate shaft 351 nonrotatablyrelative thereto. A second intermediate shaft 354 extendinglongitudinally of the vehicle body is positioned to the rear of thefirst intermediate shaft 351 and supported by the casing extension 311.A gear 355 meshing with the gear 353 and a gear 356 disposed to the rearof the gear 355 are supported by the second intermediate shaft 354nonrotatably relative thereto. The gear 356 is in mesh with a gear 357supported by a rear wheel drive output shaft 350 with a one-way clutch358 provided therebetween. Thus a power transmission mechanism for therear wheel drive output shaft 350 is provided by the output shaft 33,first intermediate shaft 351 connected to the shaft 33 nonrotatablyrelative thereto, second intermediate shaft 354 coupled to the firstintermediate shaft by the gears 353 and 355, gears 356, 357, and one-wayclutch 358.

In the present embodiment, the one-way clutch 358 is provided betweenthe output shaft 350 and the gear 357 so as to deliver a drive force tothe rear wheels only in the case where the rear wheels are subjected toa load greater than is predetermined, for example, owing to a skid ofthe front wheels and to thereby prevent the skid of the rear wheels fromroughing the terrain. In other words, if four-wheel drive is resorted toat all times, the rear wheels serving as steerable wheels will skidowing to the turning radius difference between the front wheel and therear wheel when the vehicle is turned, consequently roughing theterrain. In contrast, the present embodiment incorporates the one-wayclutch 358, which enables the rear wheels to drive the vehicle in theevent of the rear wheels skidding while precluding such a drawback.

Further according to the present embodiment, the transmission casingextension 311 is removable from the transmission main body 310. Thispermits use of common parts for two-wheel drive vehicles and four-wheeldrive vehicles. Stated more specifically, the transmission casingextension 311 may be additionally attached to the casing main body 310serving as a standard part when there arises a need to take off the rearwheel driving force. This lessens the burden of stock management ofparts and ensures greater ease in altering the specifications ofvehicles.

The following advantage can be obtained by the foregoing arrangementwherein the front end of the motor shaft 23 a is coupled to thedifferential gear unit 10 and the rear end thereof is made to projectrearward from the housing 21. The transmission is indispensable ifprovided between the HST and the differential gear unit to dividedlyprovide the front wheel driving force and the rear wheel driving forcewithin the transmission as shown in FIG. 15.

On the other hand, when the motor shaft 23 a is adapted to deliver thefront wheel driving force and the rear wheel driving force respectivelyfrom the front end and rear end thereof as shown in FIG. 4, thetransmission need not always be provided if the transmission ratio isadjusted appropriately. This leads to a cost reduction and gives thevehicle higher reliability due to a decrease in the number of parts.Since the rear wheel driving force is taken off from behind the HST 20where considerable space is available, the vehicle can be assembled withan improved efficiency. Further because the rear wheel driving force isdelivered from the rear end of the motor shaft 23 a, the connecting rodused therefor and connected to the rear axles can be shortened.

Lubricating Oil Channels

With reference to FIG. 8, the present embodiment further has a lubricantintake channel 51 for holding the interior of the housing 21 incommunication with the interior of the case 24 b, and a lubricantdischarge channel 52 for holding the interior of the case 24 b incommunication with the casing 12 for the differential gear unit.

The intake channel 51 communicates with the interior of the case 24 b inthe vicinity of the meshing point of gears in the rear wheel output unit24 and at a position downstream from the gears providing the meshingpoint with respect to the directions of rotation thereof when thevehicle is driven forward. On the other hand, the discharge channel 52communicates with the interior of the case 24 b in the vicinity of themeshing point and at a position upstream from the gears providing themeshing point with respect to the directions of rotation thereof.According to the present embodiment, in the vicinity of the meshingpoint 530 of the input gear 24 f and the intermediate gear 24 g as shownapparently in FIG. 8, the intake channel 51 and the discharge channel 52are caused to communicate with the case 24 b respectively at a positiondownstream from and at a position upstream from these gears with respectto the directions of rotation thereof for forward driving. This makesthe lubricating oil in the rear wheel drive unit 24 serviceable also asthe hydraulic fluid for the HST 20 while inexpensively and effectivelypreventing the rise in the temperature of the HST hydraulic fluid. Thereason is as follows.

First, the flow of oil within the case 24 b in the vicinity of themeshing point will be considered. For example, assuming that the inputgear 24 f rotates counterclockwise in FIG. 8 for forward travel of thevehicle, the intermediate gear 24 g meshing with the gear rotatesclockwise. Accordingly, the rotation of the input gear 24 f and theintermediate gear 24 g causes the oil to flow inwardly of the case 24 b(as indicated by the arrow X in FIG. 8) at the downstream side of thegears 24 f, 24 g with respect to the directions of rotation thereof. Atthe upstream side of the gears 24 f, 24 g with respect to the directionsof rotation thereof, on the other hand, the oil flows outwardly of thecase 24 b (as indicated by the arrow Y in FIG. 8) with the rotation ofthe gears 24 f, 24 g. If the intake channel 51 and the discharge channel52 are positioned at the downstream side and at the upstream side,respectively, with respect to the directions of rotation as describedabove, it therefore becomes possible for the pumping action afforded bythe rotation of the gears 24 f, 24 g to efficiently introduce thehydraulic fluid from the housing 21 into the case 24 b and toefficiently discharge the lubricating oil from the case 24 b. Thechannels are thus positioned based on the rotation for the forwardtravel because the vehicle is driven forward usually for longer periodsof time than reversely.

Although the positions where the intake channel 51 and the dischargechannel 52 communicate with the case 24 b are determined based on theinput gear 24 f and the intermediate gear 24 g according to the presentembodiment, the communication positions may of course be determinedbased on any of the gears within the case 24 b. For example, the intakechannel 51 can be disposed downstream from the gears 24 f, 24 g withrespect to the directions of rotation thereof, and the discharge channel52 upstream from the intermediate gear 24 g and the outer wheel 243 withrespect to the directions of rotation thereof.

To achieve an improved intake-discharge efficiency, it is desire thatthe intake channel 51 be opened to the case 24 b at the upper side ofthe meshing point of the gears, and that the discharge channel 52 beopened to the case 21 at the lower side of the meshing point of thegears. This facilitates the flow of oil from the housing 21 into thecase 24 b, further facilitating the discharge of oil from an upperportion of the differential gear unit 110 through an oil channel 52 aformed in the upper wall of the housing (see FIG. 10), consequentlymaking it possible to effectively use the oil discharged from the case21 as the lubricant for the differential gear unit.

The discharge channel 52, which is in communication with the casing 12of the differential gear unit, can alternatively be made to communicatewith the housing 21. In this case, the oil taken into the case 24 b fromthe housing 21 and given a higher temperature by being used as lubricantwithin the limited space of the case 24 b is returned to the HST 20again, consequently raising the temperature of the oil within thehousing 21. The rise in the oil temperature would entail a pressurevariation of the HST hydraulic fluid but is avoidable by providing adevice for cooling the oil in the housing 21.

According to the present invention, however, the oil taken in from thehousing 21 and used as the lubricant is discharged to the differentialgear unit 10, then drawn off from the unit 10 by the charge pump 55through a filter 54 (see FIGS. 9 to 11) and returned to the hydrauliccircuit of the HST 20. The oil becoming heated to a high temperature bybeing used as the lubricant for the rear wheel output unit is thusrecycled, whereby the oil can be cooled spontaneously. The presentembodiment therefore need not be provided with the cooling device.

The rear wheel output unit 24 is housed in the case 24 b which isremovably attached to the HST housing 21 according to the presentembodiment, whereas the invention is not limited to the embodiment. Forexample as shown in FIG. 16, the rear wheel output unit 24 canalternatively be accommodated in a space defined by a bulging portion210′ formed at the right side of the HST housing and a closing member211′ removably attached to the housing 21′. The bulging portion 210′formed on the HST housing and the closing member 211′ of thismodification correspond to the case 24 b of the present embodiment.

The relationship between the left side and the right side involved inthe present embodiment can of course be reversible.

Details of PTO Unit

The PTO unit 40 comprises the PTO shaft 41, hydraulic clutch 45 foron/off-controlling the PTO shaft, charge pump 55 for supplying ahydraulic fluid to the clutch, and hydraulic circuit for connecting theclutch 45 to the charge pump 55.

The PTO shaft 41 is supported by the front wall of the housing extension21 b and the closing member 21 c to extend longitudinally of thevehicle, and has a front end projecting forward from the front wall ofthe extension 21 b. As shown in FIG. 11, the PTO shaft 41 has an oilchannel 41 a extending axially thereof for causing a rear end portionsupported by a bearing on the closing member 21 c to communicate with aregion supporting the clutch 45. The oil channel 41 a has an opening inthe outer surface of the shaft 41 in the clutch supporting region.

With reference to FIG. 5, the hydraulic clutch 45 comprises a drivemember 43 supported by the PTO shaft 41 rotatably but axiallynonslidably and connected to the gear 22 c, a driven member 42 supportedby the PTO shaft, and a biasing member 44 for biasing these members awayfrom each other.

The drive member 43 has a plurality of friction plates 43 a looselyfitted around the PTO shaft 41, and a gear 43 b nonrotatably attached tothe plates and meshing with the gear 22 c of the hydraulic pump 22. Onthe other hand, the driven member 42 has a main body 42 a in the form ofa disk and supported by the PTO shaft 41 nonrotatably and axiallynonslidably, a second member 42 b positioned between the main body 42 aand the driven member 43 and supported by the main body 42 anonrotatably but axially slidably. The main body 42 a is formed with anoil channel 42 c for causing the oil channel 41 a formed in the PTOshaft 41 to communicate with the second member 42 b. The second member42 b has a plurality of friction plates 42 d engageable with thefriction plates 43 a.

The present embodiment further has a brake mechanism 46 provided in thehousing extension 21 b. As shown in FIG. 5, the brake mechanism 46comprises brake members 46 a supported by the front wall of the housingextension 21 b, brake disks 46 b positioned between the brake members 46a and the main body 42 a and nonrotatably supported by the PTO shaft 41,and a coupling member 46 c positioned between the brake disks 46 b andthe main body 42 a and nonrotatably supported by the PTO shaft 41 so asto be slidable axially of the shaft 41 with the sliding movement of thesecond member 42 b. The brake mechanism 46 thus constructed is releasedwhen the clutch 45 is engaged, or actuated when the clutch 45 isdisengaged. The operation of the clutch 45 and the brake mechanism 46will be described later in detail.

At the front side of the hydraulic block 80, the charge pump 55 has acasing 66 (FIG. 12) surrounding the forward projection of the pump shaft22 a liquid-tightly as shown in FIG. 5. The pump 55 is adapted to effecta pumping action by the rotation of the pump shaft 22 a.

FIG. 12 is a view in section taken along the line XII—XII in FIG. 4. Asshown apparently in FIG. 12, the charge pump 55 has an intake circuit 65b and a discharge circuit 65 a.

The intake circuit 65 b has a second suction passageway 62 (see FIGS. 5and 12), and a first suction passageway 61 formed in a thick wallportion of casing rear wall of the differential gear unit 10 so as tocommunicate with the second suction passageway 62. The first passageway61 communicates with the interior of the casing of the differential gearunit 10 through an oil filter 82 (see FIGS. 3 and 10). Through thisarrangement, the oil within the casing of the gear unit 10 is filteredby the oil filter 82, then passed through the first and secondpassageways 61, 62 and fed to the charge pump 55.

The discharge circuit 65 a of the charge pump 55 is formed in the casing66 and provided with a flow dividing member 670 (See FIG. 5) fordividedly supplying the discharged oil to the HST 20 and the hydraulicclutch 45. A pressure reduction valve is used as the flow dividingmember 670 in the present embodiment. The reduction valve supplieshydraulic fluid of predetermined pressure to the HST 20 and suppliesdrain oil to the clutch 45. Indicated at 670′ in the drawing is a reliefvalve for maintaining the discharge circuit 65 a of the charge pump at aconstant value.

The hydraulic fluid is supplied to the clutch 45 through an oil channel67 a provided at the drain side of the pressure reduction valve 670. Thehydraulic fluid is supplied to the HST 20 through an oil channel 71 aprovided at the secondary side of the pressure reduction valve 670.

FIG. 11 is a view in section taken along the line XI—XI in FIG. 4. Asshown apparently in FIG. 11, the oil channel 67 a communicates with anoil channel 67 d formed in the closing member 21 c via an oil channel 67b formed in the hydraulic block 80 and an oil channel 67 c formed in thelower wall of the housing 21.

Thus, the hydraulic fluid supply channel from the charge pump 55 to theclosing member 21 c is so formed as to extend through the housing 21.This effectively prevents the leakage of oil from the supply channel,further giving improved durability to the supply channel. If piping isprovided externally of the housing for supplying the hydraulic fluidfrom the charge pump 55 to the closing member 21 c, the piping is leftexposed and likely to become damaged or flawed, whereas when the supplychannel is made to extend through the housing 21 as in the presentembodiment, such a drawback is avoidable.

The oil channel 67 d is made to extend into an oil channel 67 e or oilchannel 72 b selectively by a directional selecting valve 75. Thus, theoil channel 67 d is caused to communicate with one of the oil channels67 e and 72 b selectively by the selecting valve 75. A solenoid valve isused as the directional selecting valve in the present embodiment.

As apparently shown in FIG. 11, the oil channel 67 e has a downstreamend extending to the rear end of the PTO shaft 41 and communicating withthe oil channel 41 a formed in the shaft 41, the shaft 41 beingsupported by the bearing on the closing member 21 c. Accordingly, whenthe oil channel 67 d is caused to communicate with the oil channel 67 eby the directional selecting valve 75, the oil discharged from thecharge pump 55 acts on the hydraulic clutch 45 by way of the oilchannels 41 a and 42 c. On the other hand, the oil channel 72 b has adownstream end communicating with the interior of the housing 21.Accordingly, when the oil channel 67 d is caused to communicate with theoil channel 72 b by the directional selecting valve 75, the oildischarged from the charge pump 55 is sent into the housing 21.

The oil channel 67 e is further provided with a hydraulic shockabsorbing member 69. According to the present embodiment, an accumulatoris used as the shock absorbing member 69. As seen in FIG. 11, theaccumulator comprises an oil channel 69 a having an upstream end incommunication with the oil channel 67 e and a downstream end incommunication with the interior of the housing 21, a slide member 69 bslidable along the oil channel 69 a, and a biasing member 69 c forbiasing the slide member 69 b toward the upstream end of the oil channel69 a. The shock absorbing member 69 thus constructed prevents thehydraulic fluid from the charge pump 55 from acting on the hydraulicclutch 45 abruptly to ensure smooth engagement of the clutch 45.

Stated more specifically, when the hydraulic fluid from the charge pump55 is sent into the oil channel 67 e as selected by the directionalselecting valve 75, the fluid flows toward the clutch 45 and also intothe oil channel 69 a, pushing the slide member 69 b against the biasingforce of the biasing member 69 c. The slide member 69 b is slidinglymoved to a position where the pressure of the fluid in the oil channel68 e is brought into balance with the biasing force of the member 69 cand comes to a halt at this position. The pressure of the hydraulicfluid acting on the clutch 45 through the oil channel 67 e will risegradually while the slide member 69 b is moved to the position ofbalance. Thus the provision of the shock absorbing member 69 preventsthe hydraulic fluid of high pressure from abruptly acting on the clutch45, with the result that the clutch 45 can be engaged smoothly.

With the present embodiment described, the aforementioned hydrauliccircuit is provided by the discharge circuit 65 a formed in the casing66 of the charge pump 55, flow dividing member 670 provided in thedischarge circuit 65 a, oil channel 67 a communicating at its upstreamend with the drain side of the flow dividing member 670, oil channel 67b formed in the hydraulic block 80 in communication with the oil channel67 a, oil channel 67 c formed in the lower wall of the housing 21 incommunication with the oil channel 67 b, oil channel 67 d formed in theclosing member 21 c in communication with the oil channel 67 c,directional selecting valve 75 provided in the oil channel 67 d, oilchannel 67 e selectively brought into or out of communication with theoil channel 67 d by the selecting valve, oil channel 41 a formed in thePTO shaft 41 in communication with the oil channel 67 e, and oil channel42 c formed in the main body 42 a in communication with the oil channel41 a.

Next, a description will be given of the operation of the hydraulicclutch 45 and the brake mechanism 46. FIG. 14 is a hydraulic circuitdiagram of the present embodiment. With reference to FIG. 14, thedischarge circuit 65 a of the charge pump is maintained at a constantpressure by the relief valve 670′. The oil supply channel 71 a leadingto the HST 20 has its pressure controlled by the pressure reductionvalve 670. On the other hand, the drain oil of the valve 670 flowsthrough the oil channel 67 a and then through the oil channel 67 b andoil channel 67 c which communicate with the channel 67 a and flows intothe oil channel 67 d formed in the closing member 21 c (see FIGS. 4 and11). As previously stated, the oil channel 67 d is divided into the oilchannel 67 e and the oil channel 72 b by the directional selecting valve75.

When a driving force is to be delivered from the PTO shaft 41, the oilchannel 67 d is brought into communication with the oil channel 67 e bythe valve 75. This causes the oil discharged from the charge pump 55 topass through the oil channel 67 e, the oil channel 40 a in the PTO shaft41 and the oil channel 42 c in the main body 42 a and act on thehydraulic clutch 45. The oil sent out from the oil channel 42 c pressesthe second member 42 b against the drive member 43 against the biasingforce of the biasing member 44 as apparently shown in FIG. 11, wherebythe driven friction plates 42 d of the second member 42 b are broughtinto engagement with the drive friction plates 43 a of the drive member43. Since the drive member 43 is coupled to the gear 22 c nonrotatablysupported by the pump shaft 22 a as previously described, a drivingforce is delivered from the drive member 43 to the second member 42 b byvirtue of the engagement of the friction plates of the two members.Since the second member 42 b is made nonrotatable relative to the mainbody 42 a, which is nonrotatable relative to the PTO shaft 41, thedriving force delivered to the second member 42 b is transmitted to thePTO shaft 41. In this way, the driving force is output from the PTOshaft 41.

In the case where the driving force is thus output from the PTO shaft41, with the hydraulic clutch engaged, the brake mechanism 46 is off.Stated more specifically, when the second member 42 b is slidingly movedrearward (rightward in FIG. 11) against the force of the biasing member44, the coupling member 36 c is also slidingly moved rearward with thismovement, consequently producing no braking force between the brakemember 36 a and the brake disk 36 b and releasing the brake mechanism36.

In the case where no driving force is to be output from the PTO shaft,on the other hand, the oil channel 67 d is caused to communicate withthe oil channel 72 b by the directional selecting valve 75, therebypermitting the oil discharged from the charge pump 55 to return to theinterior of the housing 21 through the oil channel 72 b. The clutch 45consequently blocks the power, and the brake mechanism 46 is actuated.Since no oil from the charge pump 55 acts on the clutch 45, the secondmember 42 b is slidingly moved forward (leftward in FIG. 11) by theforce of the biasing member 44. Accordingly, the driven friction plates42 are brought out of engagement with the drive friction plates 43 b,thereby interrupting power transmission from the drive member 43 to thedriven member 42. On the other hand, the forward movement of the secondmember 42 b causes the coupling member 46 c to press the brake disk 46 bagainst the brake member 46 a, producing frictional resistance betweenthe member 46 a and the disk 46 b to actuate the brake mechanism 46.

With the present embodiment, the PTO shaft 41 in rotation can be broughtto a halt by the brake mechanism 46 upon disengagement of the hydraulicclutch 45. When the transmission of power to the PTO shaft 41 inrotation is cut off by the clutch 45 in the absence of the brakemechanism 46, the PTO shaft 41 fails to stop rotating immediately owingto a force of inertia. Accordingly, a mower or the like will be held inrotation despite the disengagement of the clutch 45. This drawback isavoidable by the provision of the brake mechanism 46, which brakes thePTO shaft 41 simultaneously with the interruption of power transmissionto the PTO shaft 41.

In addition to the various advantages described, the followingadvantages are available by the PTO unit 40 thus constructed. Invehicles wherein the power from a drive source installed in the vehiclebody is transmitted to a travel device and a PTO unit via an HST 20disposed at the front side of the drive source, the PTO unit describedcomprises the PTO shaft 41, hydraulic clutch 45, charge pump 55 andhydraulic circuit. The charge pump 55 is provided at the front side ofthe HST 20, and the PTO shaft 41 and the clutch 45 are accommodated inthe housing extension 21 b of the HST 20. This arrangement provides alongitudinal distance between the drive source and the HST whileshortening the overall length of the vehicle, further permittingprovision of the PTO shaft 41 at the rear side of the vehicle body. ThePTO shaft 41 as positioned toward the rear makes it possible to diminishthe inclination angle of the transmission shaft interconnecting the PTOshaft 41 and the work device such as mower while reducing the overalllength of the vehicle including the work device. This obviates anincrease in the noise to be produced by the joints of the transmissionshaft and impairment of the durability of the joints.

Further because the flow dividing member 670 and the directionalselecting member 75 constituting the hydraulic circuit are arranged inthe charge pump casing 66 and the closing member 21 c, respectively, theoil channels around these members can be formed easily. The casing 66and the closing member 21 c are smaller than the housing 21 or hydraulicblock 80 and can therefore be bored with greater ease than the housing21 or block 80.

With the present embodiment, the oil channel 67 c is formed by boringthe housing lower wall, whereas a pipe 67 c′ can alternatively beinserted through the housing 21 as seen in FIG. 17.

Although the present embodiment has been described with reference to acase wherein the PTO shaft is made to project forward, the shaft can beprojected rearward.

Further relationship between the left and the right involved in thepresent embodiment can of course be reversed.

Pressure Oil Supply System

The preferred embodiment of pressure oil supply system according to theinvention will be described below with reference to the accompanyingdrawings. The present embodiment, i.e., pressure oil supply system 1, isadapted, for example, for use in the vehicle of FIG. 1 which comprises ahydraulic device having its operation controlled with pressure oil andwhich is so constructed that the power from a drive source 90 installedin the vehicle body is transmitted to drive axles 120 via an HST 20disposed closer to longitudinal one side of the vehicle than the drivesource and via a differential gear unit 10 coupled to the HST at oneside thereof toward the longitudinal side. The system serves to supplythe pressure oil to the hydraulic device. With the present embodiment,the HST 20 is coupled to the differential gear unit 10, with thehydraulic block (center section) 80 provided therebetween.

The following description will be given with reference to the frontmount mower tractor shown in FIG. 1 and already described, as thevehicle 100.

The construction of the HST, etc., which has already been described,will be further described in detail. At least one of the HST pump 22 andthe HST motor 23 of the HST is of the variable displacement type whichincludes a movable swash plate for giving a variable discharge rate.With the present embodiment, the HST pump 22 is of the variabledisplacement type having a movable swash plate 22 d, while the HST motor23 is of the fixed displacement type as shown in FIGS. 5 and 7. Theplate 22 d is coupled to the speed change pedal 112 disposed in thevicinity of the driver's seat, by means of an interlocking mechanism. Asseen in FIG. 7, the interlocking mechanism comprises a rotary shaft 26supported by the housing main body 21 rotatably about its axis andhaving an upper end extending upward through the top of a cover 27provided over the upper surface of the housing main body 21 a, aconnecting member (not shown) for connecting the arm 26 b to the upperend of the shaft 26, and an arm 28 provided inside the cover 27 andhaving one end connected to the movable swash plate 22 d and the otherend connected to the shaft 26. Inside the cover 27, the arm 28 isconnected to the shaft 26 by a torque spring 29 wound around the shaft26. The torque spring 29 serves as a return spring for biasing the swashplate 22 d toward a neutral position when the plate 22 d is inclined ina direction. According to the present embodiment, the spring 29 isenclosed with the cover 27 and therefore free from dust or the like,while the spring 29 is also protected against corrosion. Indicated at 29a in the drawing is an eccentric pin for finely adjusting the neutralposition of the movable swash plate 22 d.

The pressure oil supply system 1 of the present embodiment will bedescribed next. FIGS. 7 and 8 are a view in section taken along the lineVII—VII and the line VIII—VIII in FIG. 4, respectively.

The pressure oil supply system comprises a hydraulic pump 2 having adrive shaft 2 a and a pump case 2 b. The drive shaft 2 a is supported bya lower bulging portion 21 f of the housing extension 21 b, with one endthereof projecting outward from the housing (see FIG. 7). The bulgingportion 21 f has a bottom positioned at a lower level than that of thehousing main body. The bulging portion 21 f is internally provided witha magnet member 21 g. According to the present embodiment, the bottomwall of the bulging portion 21 f is formed with a bore communicatingwith the outside and openably closed with a drain plug 21 h. The magnetmember 21 g is supported by the plug at the portion thereof facing theinterior of the housing 21.

The pump case 2 b is attached to the housing 21 so as to liquid-tightlysurround the outwardly projecting end of the drive shaft 2 a. The pumpcase 2 b has an intake port 2 c and a discharge port 2 d (FIG. 8). Thehydraulic pump 2 thus constructed performs a pumping action by therotation of the drive shaft 2 a to draw oil in through the intake port 2c and supply the pressure oil via the discharge port 2 d.

The pressure oil supply system 1 further comprises a cooperativemechanism 3 (See FIG. 5) for dividedly transmitting to the drive shaft 2a the driving force delivered from the drive source to the pump shaft 22a, an intake line 4 (See FIG. 14) having one end communicating with theinterior of the casing 31 of the differential gear unit and the otherend in communication with the intake port 2 c of the pump case, and adischarge line 5 having one end communicating with the discharge port 2d and the other end communicating with the hydraulic device.

As shown in FIG. 5, the cooperative mechanism 3 has a pump drive gear 3a nonrotatably supported by the drive shaft 2 a within the housing 21.The pump gear 3 a is in mesh with the gear of the drive member 43. Thusaccording to the present embodiment, the cooperative mechanism 3 isprovided by the output gear 22 c supported on the pump shaft 22 a, thegear 43 b of the drive member 43 supported by the PTO shaft 41, and thepump drive gear 3 a supported by the drive shaft 2 a. The output gear 22c can be made to mesh with the pump drive gear 3 a directly to providethe cooperative mechanism 3. With the present embodiment, thecooperative mechanism 3 is of the gear type, but the invention is notlimited to this type; sprockets and a chain, or a belt is usable for thecooperative mechanism, which can therefore be of various types.

The following advantages are available by attaching the hydraulic pump 2to the housing 21 in this way. With the conventional system wherein thehydraulic pump is attached to the drive source, and the differentialgear unit casing serving as an oil tank, the distance between the pumpand the casing becomes increased, consequently entailing the problem ofoffering greater piping resistance to the intake line to reduce theoperation efficiency of the pump. The conventional system furtherrequires the use of a flexible tube or the like for the intake line andthe discharge line of the hydraulic pump to absorb the vibrationdifference between the pump additionally provided on the drive sourceand the casing, hence the problem of resulting in a cost increase.

According to the present embodiment, the hydraulic pump 2 is attached tothe housing 21, whereby the distance between the hydraulic pump 2 andthe casing 31 can be shortened to effectively prevent the impairment ofthe operation efficiency of the pump. Further because the housing 21 isconnected to the casing 31, no vibration difference occurs between thepump 2 and the casing 31 unlike the conventional arrangement,consequently eliminating the need to use a flexible tube or the like forthe intake line 4 and the discharge line 5 to achieve a cost reduction.

The hydraulic pump 2 can be attached to the rear wall of the housing 21as an advantage. The reason is that while a space is usually availablebetween the housing 21 and the drive source 90, the hydraulic pump 2, ifattached to the side wall of the housing 21, becomes projected widthwiseof the vehicle to entail the likelihood that the pump 2 will come intocontact with other article during driving.

A description will be given of the hydraulic circuit of the vehicle 100.FIG. 14 is a hydraulic circuit diagram of the vehicle, and FIG. 13 is aview in vertical section of the hydraulic block 80.

The hydraulic circuit of HST 20 will be described first. As illustrated,the HST pump 22 and the HST motor 23 are connected into a closed circuitby a pair of oil channels which are given a high pressure and a lowpressure, respectively, when the vehicle is driven forward. (Thechannels will hereinafter be referred to as the “high-pressure line” andthe “low-pressure line,” respectively.)

Extending between the high-pressure line 65 a and the low-pressure line65 b are two bypass lines, i.e., a first bypass line 50 e and a secondbypass line 50 d.

The first bypass line 50 e has connected thereto the oil channel 71 acommunicating with the secondary side of the pressure reduction valve670. Through the filter 82, the charge pump 55 draws in the oil withinthe differential gear unit casing 31 serving also as an oil tank. Thepump discharges the oil to a first bypass line 50 e through thereduction valve 670. The first bypass line 50 e is further provided, atopposite sides of its connection to the oil channel 71 a, with checkvalves 51 a, 52 a for permitting the oil to flow from the oil channel 71a into the closed circuit while preventing the oil from flowing from theclosed circuit into the oil channel 71 a.

The check valve 51 a provided at the high-pressure side between thehigh-pressure line 65 a and the connection has connected in paralleltherewith a relief valve 51 b for controlling the upper limit of oilpressure of the line 65 a. The relief valve 51 b provided prevents anabnormal rise of oil pressure in the high-pressure line 65 a in theevent of an abrupt load acting on the vehicle. On the other hand, a leakvalve 52 b for giving a wider neutral range to the HST is connected inparallel with the check valve 52 a provided at the low-pressure sidebetween the low-pressure line 65 b and the connection.

A second charge line 50 f is connected to the second bypass line 50 d.The second bypass line 50 d is further provided, at opposite sides ofits connection to the second charge line 50 f, with check valves 53, 53for permitting the oil to flow from the second charge line 50 f into theclosed circuit while preventing the oil from flowing from the closedcircuit into the second charge line 50 f. The check valves 53, 53provided compensate for the amount of working fluid within the closedcircuit when the vehicle is brought to a halt, preventing the vehicleform freewheeling. As apparently shown in FIG. 13, the check valves 53,53 have bypass pins 53 a, 53 a for forcibly bringing the high-pressureline and the low-pressure line into communication to facilitate therotation of the wheels when the HST malfunctions. For example in thecase where the vehicle is drawn in the event of the vehiclemalfunctioning, the motor shaft operatively connected to the wheels alsorotates. The rotation of the motor shaft produces a pressure differencebetween the high-pressure line and the low-pressure line. If thesepressure lines are connected only by the HST motor and the HST pump atthis time, the pressure difference remains unless the input shaft of theHST motor is rotated. Accordingly the forcible traction of the vehicleinvolves the rotation load of the HST pump input shaft and the drivesource output shaft, whereas the second bypass line, if forcibly openedby the bypass pins, brings the high-pressure line and the low-pressureline into communication, eliminating the pressure difference due to therotation of the motor shaft. Thus, the motor shaft is easily rotatableeven when the wheels are forcibly rotated as by traction, reducing theload involved in the traction.

A description will be given next of a hydraulic circuit included in thepressure oil supply system of the present embodiment and hydraulicdevices having their operation controlled by the pressure oil suppliedby the system. Indicated at 105 and 81 in FIG. 14 are a front mower liftand power steering device serving as the hydraulic devices.

As previously stated, the hydraulic pump 2 is adapted to draw in the oilwithin the casing 31 of the differential gear unit through the intakeline 4 and to supply the pressure oil to the hydraulic devices 105, 81through the discharge line 5. Preferably a filter can be provided in theintake line 4. According to the present embodiment, a downstream linefrom the filter 82 interposed between the charge pump 55 and the casing31 is branched into a hydraulic line leading to the charge pump and theintake line 4.

The power steering device 81 comprises a power steering cylinder 105 bcoupled to the steerable wheels, and a power steering valve unit 83 forcontrolling the supply of pressure oil from the discharge line 5 to thecylinder 105 b. The valve unit 83 comprises a rotary directionalselecting valve 83 a operatively connected to the steering wheel at thedriver's seat for effecting an oil channel change-over, and a reliefvalve 83 b for controlling the pressure of oil to be supplied to thecylinder 105 b.

On the other hand, the front mower lift 61 comprises a lift arm 106connected to the mower, lift cylinder 105 a connected to the lift arm,and lift valve unit 64 for controlling the supply of oil to the liftcylinder. The valve unit 64 comprises a directional selecting valve 64 aoperatively connected to the lever at the driver's seat for effecting anoil channel change-over, relief valve 64 b for controlling the pressureof oil to be supplied to the lift cylinder, needle valve 64 c forholding the pressure oil in the lift cylinder, and flow control valve 64d for preventing the presser oil from abruptly returning from the liftcylinder.

The oil returning from the power steering valve unit 83 and the liftvalve unit 64 is cooled by an oil cooler 66 disposed adjacent to aradiator 65 (see FIG. 1) and supplied to the housing 21 through an inlet21 d. After cooling the oil within the housing, the oil is returned tothe casing 31 of the differential gear unit through an outlet 21 e.

With the present embodiment as seen in FIG. 7, the inlet 21 d ispositioned at an upper portion of the housing main body 21 a, and theoutlet 21 e at an upper portion of the housing extension 21 b. Thisresults in the following advantage. The cooled oil is supplied to thehousing main body 21 a enclosing the HST pump 22 and HST motor 23therein and is drawn off from the extension 21 b extending from the mainbody 21 a toward one side widthwise of the vehicle. Within the housing21, the oil therefore flows from the main body 21 a toward the extension21 b. The cooled oil can accordingly be circulated through the entirehousing to efficiently cool the interior of the housing. The extensionof the housing 21 has the bulging portion 21 f at its lower portion,with the magnet member 21 g provided in the bulging portion, so thatiron particles entrained in the flow of oil can be held in the bulgingportion 21 f. This effectively precludes the HST pump and motor frommalfunctioning due to the presence of iron particles.

The hydraulic device to be installed in the vehicle has been describedwith reference to the lift for the mower disposed in front of thevehicle body and to the power steering device according presentembodiment, whereas the invention is not limited to the embodiment butcan be applied to various hydraulic devices, nor is the inventionlimited by the position where the hydraulic device is installed.

Other Embodiments of Transmission Mechanism

Another preferred embodiment of transmission mechanism of the inventionwill be described with reference to FIG. 18. FIG. 18 is a plan view indevelopment and in section of the transmission mechanism of theembodiment. Throughout the drawings, like parts or corresponding partswill be designated by like numerals or symbols and will not be describedrepeatedly.

In place of the transmission casing main body 31 a and the HST housing21 included in the transmission mechanism of the foregoing embodiment,these components are integrally made into a casing 300 according to thepresent embodiment.

The transmission mechanism thus constructed has the same advantages asthe preceding embodiment and attains a further reduction in cost due toa decreased number of parts used.

For the integral casing 300 to accommodate therein the differential gearunit 10, travel cooperative mechanism, HST 20 and PTO cooperativemechanism according to the present embodiment, the oil-channel block 80is disposed to the rear of the HST, and a gear 22′ is positioned infront of the hydraulic pump main body and in engagement with thehydraulic clutch 45 providing the PTO cooperative mechanism.

The present invention is not limited to the embodiments described butcan be modified variously within the scope of technical concept as setforth in the appended claims.

For example, although the embodiments have been described with referenceto a front mount mower tractor, the invention is applicable not only tosuch tractors but also to various work vehicles equipped with a workdevice externally of the vehicle body at the front or rear side thereof.

Although gears are used for the cooperative mechanisms in the foregoingembodiments, the invention is not limited to such mechanisms, butvarious mechanical cooperative mechanisms comprising, for example, achain are usable.

The differential gear unit, transmission and HST are arranged in theapproximate center of the vehicle body with respect the widthwisedirection thereof in view of the balance of the vehicle, whereas theinvention is not limited to such an arrangement. Insofar as thesecomponents are arranged in the order mentioned, these components can bearranged at different positions with respect to the widthwise direction.

ADVANTAGES OF THE INVENTION

The transmission mechanism embodying the first feature of the presentinvention comprises a travel power transmission path for transmittingpower from a drive source through a HST to a differential gear unit fordriving axles positioned toward a first direction, and a PTO powertransmission path for dividedly transmitting power from the travel powertransmission path to a PTO shaft for driving a work vehicle, atransmission being disposed between the differential gear unit and theHST to provide the travel power transmission path, a housing of the HSThaving the PTO shaft projecting therefrom and transmission meansaccommodated therein and coupling the PTO shaft to a pump shaft toconstitute the PTO power transmission path. Accordingly, the PTO shaftcan be positioned toward a second direction. The transmission mechanismtherefore has a simple construction and is adapted to give a shortenedoverall length to the vehicle while permitting a transmission shaftconnecting the PTO shaft to the input shaft of the work device to bepositioned closer to a horizontal.

The HST housing has a main body accommodating a hydraulic pump and ahydraulic motor therein, and an extension extending from the main bodytoward widthwise one side of the vehicle body, the main body having anopening at a side thereof toward the first direction, the extensionhaving an opening at a side thereof toward the second direction, the PTOshaft projecting from the extension, the opening of the main body beingclosed with a hydraulic block. The block can then be shortened in lengthin the widthwise direction and becomes less costly owing to a reductionin material cost. When the HST housing has such a structure, the moldfor the main body is removable toward the first direction, and the moldfor the extension toward the second direction. This assures greater easein producing the HST housing by casting.

When the HST housing has a main body accommodating the hydraulic pumpand the hydraulic motor therein, and an extension extending from themain body toward widthwise one side of the vehicle body, with the PTOshaft projecting from the extension and with the pump shaft and themotor shaft arranged in approximately the same horizontal plane, thedrive shaft to be connected to the pump shaft can then be positioned ata lower level. This affords improved running stability to the vehicledue to the lowered center of gravity thereof.

When the casing of the transmission is adapted to accommodate thedifferential gear unit therein, a separate casing need not be providedfor the gear unit to achieve a cost reduction due to a decreasedmaterial cost.

A cost reduction due to a reduction in material cost can also beattained by making the transmission casing and the HST housing into anintegral structure.

The transmission casing may comprise a main body for accommodating atravel cooperative mechanism, and an extension extending from the mainbody toward the other widthwise side of the vehicle body, the extensionsupporting thereon an output shaft for driving axles positioned towardthe second direction and being provided with transmission means coupledto the travel cooperative mechanism. While positioning the drive sourceat a lower level to lower the center of gravity of the vehicle andthereby give improved running stability to the vehicle, thisconstruction makes it possible to position the coupling rod for thesecond-direction axles free of interference with the drive source,whereby four-wheel drive can be realized for the vehicle.

If the casing main body is made separable from the extension, the casingmain body can be prepared as a common part, such that when there arisesa need to take off a driving force for the second-direction axles, theportion of extension can be attached to the common part. This results ineasier stock management of parts, further making is possible to alterthe specifications of the vehicle with ease after shipment.

The transmission mechanism embodying the second feature of the presentinvention for use in vehicles is adapted to transmit power from a drivesource installed in the vehicle to a differential gear unit for drivingaxles positioned toward a first direction, via an HST disposed towardthe first direction from the drive source, the HST having a motor shaftwith a first-direction end projecting from a housing of the HST towardthe first direction and connected to the gear unit, the motor shafthaving a second-direction end projecting from the housing toward asecond direction. This construction eliminates the need for thetransmission to be disposed between the HST and the differential gearunit for dividing the power into a driving force for first-directionwheels and a driving force for second-direction wheels, consequentlyleading to a cost reduction. Since the transmission serving as a powertransmission path for both the driving forces need not be provided, thevehicle is given improved reliability and can be assembled with animproved efficiency.

The HST housing may be provided with a second-direction wheel outputunit extending in the second direction and positioned toward one sidewith respect to the widthwise direction of the vehicle, the output unithaving a second-direction wheel drive shaft at an end thereof toward thewidthwise side. The drive source to be installed at the second-directionside of the HST can then be positioned at a lower level. This rendersthe vehicle compact and improves the running stability of the vehicle.

The second-direction wheel output unit may be provided, at theabove-mentioned widthwise end thereof, with a bulging part, with aclutch mechanism disposed in the bulging part for permitting thesecond-direction wheels to rotate at a higher speed than thefirst-direction wheels when the vehicle is driven forward whilepermitting the first-direction wheels and the second-direction wheels torotate at the same speed when the wheel is driven reversely. An increasein the size of the vehicle is then avoidable despite the provision ofthe clutch mechanism.

When the transmission mechanism comprises an intake channel holding thehousing in communication with the case for introducing drain oil fromthe interior of the housing into the case, and a discharge channel fordischarging the oil from the case, the hydraulic fluid of the HST isusable also as lubricating oil for the second-direction wheel outputunit.

The transmission mechanism may be so constructed that the dischargechannel holds the case in communication with a casing of thedifferential gear unit, the intake channel communicating with the caseat a position downstream from a meshing point of gears constituting thecooperative mechanism with respect to the directions of rotation thegears when the vehicle is driven forward, the discharge channelcommunicating with the case at a position upstream from the meshingpoint of the gears with respect to the directions of rotation thereofwhen the vehicle is driven forward. The rise of temperature of the oilwithin the HST housing can then be effectively prevented whilepermitting the hydraulic fluid of the HST serving also as thelubricating oil for the output unit.

The transmission mechanism embodying the third feature of the presentinvention for use in vehicles is adapted to transmit power from a drivesource installed in a body of the vehicle to a travel device and a PTOunit via an HST disposed outwardly of the drive source in a longitudinaldirection of the vehicle, the transmission mechanism comprising a PTOshaft, a hydraulic clutch for effecting or interrupting powertransmission to the PTO shaft, a charge pump for supplying a hydraulicfluid to the clutch, and a hydraulic circuit for interconnecting theclutch and the charge pump, the HST comprising a housing having a mainbody accommodating the hydraulic pump and the hydraulic motor therein,and an extension extending from the main body toward one side withrespect to the widthwise direction of the vehicle, the charge pumphaving a casing liquid-tightly surrounding an outer end of the pumpshaft projecting outward longitudinally of the vehicle, the charge pumpbeing adapted to perform a pumping action by the rotation of the pumpshaft, the PTO shaft being supported by the housing extensionlongitudinally of the vehicle and having an outer end projecting outwardlongitudinally of the vehicle, the hydraulic clutch being supported bythe PTO shaft within the housing extension. The transmission mechanismtherefore serves to shorten the overall length of the vehicle, positionthe PTO shaft for driving the mower or the like longitudinally inwardlyof the vehicle and give a distance between the drive source and the HSTat the same time.

The housing may have an inner wall extending widthwise of the vehicle soas to face the drive source, opposite side walls extendinglongitudinally of the vehicle and joined to respective opposite ends ofthe inner wall each at one end thereof, and an outer wall extendingwidthwise of the vehicle and joined to the other ends of the side walls,the outer wall having an opening formed in a region thereofcorresponding to the housing main body, the inner wall having an openingformed in a region thereof corresponding to the housing extension, theopening of the outer wall being closed with a hydraulic block, theopening of the inner wall being closed with a closing member. Thehydraulic block which is disposed at one side of the housinglongitudinally outward thereof can then be diminished in size.

The hydraulic circuit comprises a flow dividing member provided in adischarge channel of the charge pump for supplying oil discharged fromthe charge pump dividedly to the HST and the hydraulic clutch, and achange-over member interposed between the flow dividing member and thehydraulic clutch for effecting or interrupting the supply of oil to thehydraulic clutch, the flow dividing member being disposed in a casing ofthe charge pump, the change-over member being disposed in the closingmember. Oil channels can then be formed by boring with ease.

When an oil channel interconnecting the flow dividing member and thechange-over member is made to extend through the housing, the channelcan be given improved durability, effectively preventing the oil fromleaking from the channel.

When a hydraulic shock absorbing member is provided in the closingmember at a position downstream from the change-over member, the powertransmission to the PTO shaft through the clutch can be effectedsmoothly.

The pressure oil supply system embodying the fourth feature of thepresent invention is for used in a vehicle which is so adapted thatpower from a drive source installed in a body of the vehicle istransmitted to drive axles via an HST disposed closer to longitudinalone side of the vehicle than the drive source and via a differentialgear device coupled to the HST at one side thereof toward said onelongitudinal side, the system comprising a hydraulic pump provided in ahousing of the HST, the differential gear device having a casing madeserviceable as an oil tank for the hydraulic pump. The system istherefore adapted to use a shortened intake line for interconnecting thehydraulic pump and the oil tank, effectively preventing the impairmentof the operation efficiency of the pump due to the piping resistance ofthe intake line. The system produces no vibration difference between thehydraulic pump and the oil tank, consequently eliminating the need touse a flexible tube or the like for the intake line to thereby achieve acost reduction.

The housing of the HST has a main body accommodating the HST pump andthe HST motor therein, and an extension extending from the main bodytoward widthwise one side of the vehicle, the extension having a bottomportion bulging downward to a lower level than a bottom portion of themain body, a magnet member being disposed within the downwardly bulgingportion of the extension. The magnet member then attracts iron particlesin the oil within the housing, whereby the HST pump and motor can beeffectively prevented from malfunctioning due to the presence of suchiron particles.

The housing main body of the HST has an inlet formed in an upper portionthereof for admitting return oil from the hydraulic device, the housingextension being formed with an outlet for recycling to the casing theportion of oil contained in the housing in excess of a predeterminedamount. The oil within the housing can be caused to flow from the mainbody toward the extension, whereby iron particles can be effectivelyattracted by the magnet member.

When the return oil is used as a cooling oil, the oil within the housingcan be cooled effectively.

When the hydraulic pump is attached to the housing at a side thereoftoward the other longitudinal side of the vehicle, the pump will notproject outward widthwise of the vehicle and can be effectivelyprecluded from coming into contact with other article during driving.

1. A transmission mechanism for a work vehicle, comprising: ahydrostatic transmission (HST) including a hydraulic pump having a pumpshaft for receiving power from the drive source of the vehicle, ahydraulic motor having a motor shaft rotatable in cooperation with thehydraulic pump, and an HST housing accommodating the hydraulic pump andthe hydraulic motor therein; and a power take-off (PTO) powertransmission path disposed within the HST housing for dividedlytransmitting the power from the pump shaft of the HST to a PTO unit fordriving a work device, the PTO unit comprising a PTO shaft being placedopposite the motor shaft with the pump shaft being therebetween andsupported by the HST housing so as to extend outwardly from the HSThousing, and a PTO cooperative mechanism accommodated in the HST housingand coupling the pump shaft to the PTO shaft to provide the PTO powertransmission path.
 2. The transmission mechanism of claim 1, wherein thePTO shaft, directed toward a front axle, is disposed in the rear of thefront axle.
 3. A transmission mechanism for a work vehicle, comprising:a hydrostatic transmission (HST) including a hydraulic pump having apump shaft for receiving power from the drive source of the vehicle, ahydraulic motor having a motor shaft rotatable in cooperation with thehydraulic pump, and an HST housing accommodating the hydraulic pump andthe hydraulic motor therein; a power take-off (PTO) power transmissionpath disposed within the HST housing for dividedly transmitting thepower from the pump shaft of the HST to a PTO unit for driving a workdevice, the PTO unit comprising a PTO shaft being placed opposite themotor shaft with the pump shaft being therebetween and supported by theHST housing so as to extend outwardly from the HST housing, and ahydraulic clutch for effecting or interrupting power from the pump shaftto the PTO shaft; a charge pump for supplying a hydraulic fluid to theclutch; and a hydraulic circuit for interconnecting the clutch and thecharge pump.
 4. The transmission mechanism of claim 3, wherein the PTOshaft, directed toward a front axle, is disposed in the rear of thefront axle.
 5. A transmission mechanism for a work vehicle, comprising:a hydrostatic transmission (HST) including a hydraulic pump having apump shaft for receiving power from the drive source of the vehicle, anda hydraulic motor having a motor shaft rotatable in cooperation with thehydraulic pump; and a power take-off (PTO) power transmission path fordividedly transmitting the power from the pump shaft of the HST to a PTOunit for driving a work device, the PTO unit comprising a PTO shaft anda hydraulic clutch for on/off-controlling the PTO shaft, wherein the PTOshaft is supported by the housing such that the PTO shaft is parallel tothe pump shaft, wherein the pump shaft is connected with the PTO shaftvia the hydraulic clutch supported by the PTO shaft and meshing gearsconnecting the drive member of the clutch and the pump shaft, whereinthe hydraulic pump and the hydraulic clutch are located on the same sidein relation to the meshing gears, and wherein the pump and the hydraulicclutch are accommodated in a common housing and constructed so as to bedriven by a common input shaft.
 6. The transmission mechanism of claim5, wherein the pump and the hydraulic clutch are together arrangedperpendicularly to the vehicle's normal movement.